1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to a transfiective LCD device and a method of manufacturing the same.
2. Description of Related Art
In general, LCDs are divided into transmissive LCD devices and reflective LCD devices according to whether the display uses an internal or an outer light source.
A typical transmissive LCD device comprises a liquid crystal panel and a back light device. The liquid crystal panel includes upper and lower substrates with a liquid crystal layer interposed therebetween. The upper substrate has a color filter, and the lower substrate has a thin film transistor (TFT) as a switching element. An upper polarizer is arranged on the upper substrate of the liquid crystal panel, and a lower polarizer is arranged between the lower substrate of the liquid crystal panel and the backlight device.
At this time, the two polarizers have a transmittance of 45%, the two substrates have a transmittance of 94%, the TFT array and the pixel have a transmittance of 65%, and the color filter has a transmittance of 27%, respectively. Therefore, the transmissive LCD device gets to have about a transmittance of 7.4% as seen in FIG. 1 which shows a transmittance respectively measured after light passes through each layers. For such a reason, the transmissive LCD device requires a high brightness of the back light device, and thus an electric power consumption by the backlight device increases. In order to supply a sufficient power to the backlight device, a relatively heavy battery is employed, however, there still exists a problem that the battery can not be used for a long time.
In order to overcome the problem described above, the reflective LCD has been developed.
FIG. 2 is a plan view illustrating a typical reflective LCD device. As shown in FIG. 2, the reflective LCD device 100 includes gate lines 6 and 8 arranged in a transverse direction, data lines 2 and 4 arranged in a longitudinal direction perpendicular to the gate lines 6 and 8, and thin film transistors(TFTs), for example, the thin film transistor xe2x80x9cSxe2x80x9d near a cross point of the gate line 8 and the data line 2. Each of the TFTs xe2x80x9cSxe2x80x9d has a gate electrode 18, a source electrode 12 and a drain electrode 14. The gate electrode 18 extends from the data line 2, and the gate electrode 18 extends from the gate line 8. The reflective LCD device 100 further includes reflective electrodes 10. The reflective electrode 10 is electrically connected with the drain electrode 14 through a contact hole 16 and is made of a metal having a good reflectance.
FIG. 3 is a cross sectional view taken along the line xe2x96xa1xe2x80x94xe2x96xa1 of FIG. 2. As shown in FIG. 3, the gate electrode 18 is formed on the substrate 1, and a gate insulating layer 20 is formed on the exposed surface of the substrate 1 while covering the gate electrode 18. A semiconductor layer 22 as an active area of the TFT xe2x80x9cSxe2x80x9d is formed over the gate electrode 18. The source and drain electrodes 12 and 14 are spaced apart from each other. The source electrode 12 overlaps one end portion of the semiconductor layer 22, and the drain electrode 14 overlaps the other end portion of the semiconductor layer 22. A passivation film 24 is formed over the whole surface of the substrate 1 while covering the TFT xe2x80x9cSxe2x80x9d. The passivation film 24 has the contact hole 16 on the predetermined portion of the drain electrode 14. The reflective electrode 10 is formed on the passivation film 24 and is electrically connected with the drain electrode 14 through the contact hole 16.
Since the reflective LCD device uses ambient light, it is easy to carry. Also, the reflective LCD device is superior in aperture ratio to the transmissive LCD device. By the way, the reflective LCD device has a problem that it is affected by its surroundings. For example, the brightness of ambient light in an office differs largely from that of the outdoors. Also, even in the same location, the brightness of ambient light depends on the time of day (e.g., noon or dusk). Therefore, the reflective LCD device can not be used at night without ambient light.
For the foregoing reasons, there is a need for a transflective LCD device that can be used on the time of day as well as night.
To overcome the problems described above, preferred embodiments of the present invention provide a transflective LCD device manufactured by a simplified process.
In order to achieve the above object, the preferred embodiment of the present invention provides a trasflective liquid crystal display device including a first substrate having a color filter; a second substrate having: a) a gate electrode formed on the second substrate; b) a first insulating layer formed on the exposed surface of the second substrate while covering the gate electrode; c) a semiconductor layer formed on the first insulating layer and over the gate electrode; d) a source electrode overlapping one end portion of the semiconductor layer; e) a drain electrode overlapping the other end portion of the semiconductor layer and spaced apart from the source electrode; f) a second insulating layer formed on the exposed surface of the first insulating layer while covering the source and drain electrode, having a first contact hole formed on a portion of the drain electrode; g) a pixel electrode formed on the second insulating layer and electrically connected with the drain electrode through the first contact hole; h) a third insulating layer on the pixel electrode and having a second contact hole over the first contact hole; and i) a reflective electrode formed on the third insulating layer and having a light transmitting hole and electrically connected with the pixel electrode through the second contact hole, the light transmitting hole transmitting light and covered by the pixel electrode; a liquid crystal display layer interposed between the first and second substrates; and a back light device for supplying light and located under the second substrate.
In another aspect, the preferred embodiment of the present invention a trasflective liquid crystal display device including: a first substrate having a color filter; a second substrate having: a) a gate electrode formed on the second substrate; b) a first insulating layer formed on the exposed surface of the second substrate while covering the gate electrode; c) a semiconductor layer formed on the first insulating layer and over the gate electrode; d) a source electrode overlapping one end portion of the semiconductor layer; e) a drain electrode overlapping the other end portion of the semiconductor layer and spaced apart from the source electrode; f) a second insulating layer formed the exposed surface of the first insulating layer while covering the source and drain electrode, having a first contact hole formed on a portion of the drain electrode; g) a reflective electrode formed on the second insulating layer and electrically connected with the drain electrode through the first contact hole and having a light transmitting hole, the light transmitting hole transmitting light; h) a third insulating layer on the reflective electrode and having a second contact hole over the first contact hole; and i) a pixel electrode formed on the third insulating layer and electrically connected with the reflective electrode through the second contact hole and having a sufficient size to cover the light transmitting hole; a liquid crystal display layer interposed between the first and second substrates; and a back light device for supplying light and located under the second substrate.
The reflective electrode is made of an opaque metal, and the pixel electrode is made of a transparent conductive material such as indium tin oxide and indium zinc oxide. The first and third insulating layers are made of one of SiNx and SiOx. The second insulating layer is made of benzocyclobutene (BCB). The light transmitting hole is formed on the central portion of the reflective electrode, or The reflective electrode is formed in the form of an island so that the reflective electrode is surrounded by the transmitting hole. The transflective liquid crystal display device further includes upper and lower polarizers. The upper polarizer is arranged over the first substrate, and the lower polarizer is arranged between the second substrate and the backlight device.